The present invention relates to a signal transmission technique, and in particular to a transmission method and a transmission apparatus responsive to the phase error for controlling the receiving sample timing of a signal which does not include a special signal or signal train for phase detection.
In a conventional apparatus, intersymbol interference of a received signal is first eliminated to sample the received signal and phase detection is performed by using a special signal train (training pattern) included in the received signal as described in National Telecommunications Conference, E1.5.1-6, Nov. 1981.
In general, structures of signal frames in a transmission path are restricted by standards of respective nations. Particularly standard specifications (ANSI standards) of the USA forbids a transmission frame to include a special signal train for phase detection. As reported by Hayashi etc. in Technical Report CS88-38, pp. 13-18, The Institute of Electronics, Information and Communication Engineers (IEICE), Japan, July 1988, therefore, residual intersymbol interference due to a receiver causes a phenomenon described below. That is to say, the phase detector has a plurality of convergence points and the phases at which the received signal is sampled converges into a quasi-stable point. Once quasi-convergence has occurred, it is impossible to escape from the receiving phase. This results in a problem of increase of initial convergence or a problem of failure in convergence caused by nonconvergence.